using System;

using System.Linq;

using System.Collections.Generic;

public class Program

{

    static IEnumerable<IEnumerable<T>> GetPermutations<T>(IEnumerable<T> list, int length)

    {

        if (length == 1) return list.Select(t => new T[] { t });

​

        return GetPermutations(list, length - 1)

            .SelectMany(t => list.Where(e => !t.Contains(e)),

                        (t1, t2) => t1.Concat(new T[] { t2 }));

    }

    public static void Main()

    {

        char[] aakkoset = new[] {'a', 'b', 'c'};

        foreach (var permutaatio in GetPermutations(aakkoset, 3))

        {

            Console.WriteLine(string.Join(',', permutaatio));   

        }

    }

}